In recent years, an image scanner for large reading objects is needed in the image scanner market. In order to read an image of a large reading object, a sensor is required to be elongated in a reading direction (main scanning direction). With elongation of the sensor, use of a single board for mounting a light receiving element sensor chip becomes difficult. Therefore a structure in which short length boards arrayed in a line in the reading direction is required. Small size and high accuracy of mounting distances between adjacent sensor chips of the array of sensor chips and sensor boards are important for minimizing missing portions of the reading image and increasing image quality.
Image scanners on which sensor chips are highly accurately mounted are, for example, those disclosed in Patent Literature 1 through 3. Patent Literature 1 discloses an image scanner that adjusts positions of a plurality of sensor boards. Patent Literature 2 discloses an image scanner including connection means for connecting sensor boards together to prevent damaging of a sensor chip. Patent Literature 3 discloses an image scanner in which two adjacent sensor boards are overlapped in a thickness direction to prevent damaging of a sensor chip.